The present invention relates to video signal processing, and more particularly to key priority for a mix/effect (M/E) bank having multiple keyers.
The current state of the art in production video switchers divides functionality into mix/effect (M/E) banks, each having two keyers plus a pair of background buses. As programs become more complex, the compositing capability of a four bank switcher (3 M/E banks plus a program/preset bank) is no longer sufficient. Increasing panel depth to accommodate additional M/E banks is impractical. Adding keyers to an M/E bank is a practical solution to the need for additional compositing, but complicates the specification of keyer priority. With just two keyers, one keyer is always over the other. With three or more keyers, a binary selection is not sufficient.
What is desired is a simple way to specify keyer priority for an M/E bank having more than two keyers.
Accordingly the present invention provides key priority for a mix/effect bank having multiple keyers, specifically more than two keyers. The outputs of the keyers is input to a crosspoint matrix r outer, which router provides a current stack output representing the priority of the keyers for a program video output bus and provides a next stack output representing the priority of keyers for a preview video output bus. The current and next stacks are input to respective current and next priority combiners in order of highest to lowest priority. The outputs of the combiners are input to a transition mixer, the output of which is coupled to a program video output bus via a program/preview switch, and the output of the next priority combiner is coupled to a preview video output bus via the program/preview switch. The transition mixer passes the output from the current priority combiner to the program video output bus except when the transition is made from the program output to the preview output.
The objects, advantages and other novel features of the present invention are apparent from the following detailed description when read in conjunction with the appended claims and attached drawing.